Corner balancing is more than nought the most commonly overlooked thing in the world of suspension. The definition of a corner balance is is the process of shifting the weight carried by each wheel to approach optimal values. Your ideal values should be the total weight of the car distributed evenly across all four wheels of the car. Some special applications require a different corner balance setup like 40/60 distribution with more weight in the rear. Some weight can be moved around by physical moving parts of the car (ie relocating your battery from the front to the rear, removal of spare tire, ect), but this process is mainly focused on shifting the weight of the vehicle by adjusting the spring height of each shock/coilover.
Corner balancing is usually reserved for track and racecars as it greatly affects the suspension characteristics under heavy loads. Most track cars are equipped with adjustable coilovers that simplify the job of adjusting ride height over each coilover perch, which in turn changes the weight distribution of the vehicle. Sometimes the process is as simple as adjusting your ride height, but if the weight imbalance is extreme, physically relocating or removing parts would be a way to achieve that ideal 50/50 distribution for most racers. Adding weight to your car sounds like the opposite of what you should do if you’re racing but in some cases extra weight is needed in a corner during balancing and there are numerous race cars with simply a metal plate or weight bolted to the body to dial in the weight distribution.
The actual process of corner balancing involves four specially made scales that need to be used on a perfectly flat surface to accurately read the weight distribution across the car. Adjustments are made mainly at the spring perches to adjust the ride height at each corner. These adjustments include changing the amount of weight resting over the spring perch in relation to the other three springs and is a very intuitive and time consuming process as the values for each corner change in relation to each other. When performing a corner balance you must be sure that your car is exactly the same as it would be under track conditions. The weight of the driver over the left front of the vehicle needs to be accounted for along with all of the fluids topped off or at whatever levels are optimum during competition driving. Not only does the weight distribution across left-right and front-rear planes matter, the cross weight of the car does also. You can find the cross weight of your vehicle by adding wheel values that are diagonal to each other (ex. RF tire + LR tire = cross weight) An unbalanced or improperly cross weighted car might have the tendency to understeer in a left handed corner while oversteering in right hand corners due to the amount of weight sitting on each tire during the turn being uneven.
The whole process involves a lot of trial and error along with a feel for the actual process. A lot of the benefits of corner balancing are seen with higher end and racing spec springs that usually come with higher/stiffer spring rates. Most road cars for every day use sit on springs that are softer than 300lbs/in. Adjustments on spring rates softer than this have a smaller affect on your suspension than making the same adjustments on a stiffer corner.